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A. Rock slab. The surface is pitted with pores in sites where ferromagnesian mineral
existed prior to hydrothermal alteration. Black crystals of magnetite are scattered
throughout the rock. The slab is about 2.8 x 5.5 mm. in size. DDH 407-257.6.
B. Photograph of thin-section in polarized light. Crystals of anhedral to subhedral
potassium feldspar. The black areas are pores. Scattered anhedral crystals of
hydrothermal biotite (orange). The surface is about 3.7 x 2.5 cm in size. DDH 407-257.6.
C. Photomicrograph of thin-section DDH 407-257.6. Anhedral crystals of potassium
feldspar and interstitial quartz. The field of view is about 4 x 6 mm. Plane-polar light.
D. Photomicrograph of the same area of DDH 407-257.6 shown in C. The
interstitial quartz can be more readily recognized in this photograph, which was
taken with crossed polarizers, than in Figure 21C. Several anhedral crystals of
hydrothermal biotite (orange) are visible.
E. Rock slab with heavily pitted surface (dark elongate areas). The pits contain
hydrothermal biotite and crystalline quartz and mark the sites that ferromagnesian minerals occupied prior to alteration. The orange mottling is
localized in areas of clay altered feldspar. The slab is about 3.5 x 5.5 cm. in size. JDD-94-14.
F. Photograph of thin-section in polarized light. Sample consists predominantly of
anhedral crystals of potassium feldspar and quartz. Lesser amounts of albite are
present but not easily recognized. Black areas are void spaces. The thin-section is about 2.5 x 3.8 cm. in size. JDD-94-14.
G. Photomicrograph of thin-section JDD-94-14. Anhedral potassium feldspar (frosted surface) and interstitial quartz (smooth surface). Rectangular, T-shaped crystal near the center of the photograph is albite. The field of view is about 3 x 4.3 mm. Reflected light.
H. Photomicrograph of the same area of thin-section JDD-94-14 shown in G. Faint twinning can be seen two crystals of albite. Anhedral hydrothermal biotite (orange). Crossed-polar light.
